Ring-opening polymerization of lactones or cyclic carbonates is broadly divided into two categories of polymeri-zation. The former is anionic polymerization in which organo-metallic compounds are generally employed as an initiator.
The latter is polymerization in which there are employed compounds having at least one active hydrogens such as water and alcohols which are initiators in the presence of various Lewis acids in a broad sense, which are catalysts.
In the anionic polymerization, there are employed n-butyl lithium, tert-butoxy potassium, sodium methoxide, and rare earth metal complexes, as the organometallic compounds which are initiators.
Specifically, Japanese Patent Unexamined Publication (hereinafter, referred to as Kokai) No. 37737/1971 discloses a polystyrene-polycarbonate block copolymer and the like, Kokai No. 294326/1990 (EP-A-392251) discloses a polycaprolactone-polyneopentylglycol carbonate block copolymer and the like, and further Kokai No. 500982/1993 (corresponding to U.S. Pat. Nos. 5,028,667 and 5,095,098) and Kokai No. 247184/1993 disclose processes for the preparation of polycaprolactones in which rare earth metal complexes are employed.
In the anionic polymerization processes, there is a strong point in that there can be prepared a polymer or block copolymer having a narrow molecular weight distribution by carrying out a particular reaction process in which solvents and cyclic monomers to be employed are very strictly refined.
As catalysts in the latter polymerization processes, there are exemplified various Lewis acids in a broad sense such as sulfuric acid, p-toluene sulfonic acid, quaternary ammonium salts, boron trifluorides, stannous tetrachloride, trialkyl aluminum, tetrabutyl titanate, and dibutyl tin oxide, and the like. Lewis acids have a function capable of accelerating nucleophilic property in initiators such as water and alcohols together with lowering the energy required in the ring-opening reaction of lactone monomers or cyclic carbonate monomers.
In the ring-opening reaction, although water or alcohols are employed as an initiator, they also act as a reaction terminator and a chain transfer agent, resulting in it being considerably difficult to prepare a polymer or copolymer having a narrow molecular weight distribution in comparison to a polymer prepared by an anionic polymerization.
In Macromolecules, 20, 2982-2988 (1987), Inoue and Aida et al, have reported a process in which a monodispersed lactone polymer can be prepared as an example of a polymer or block copolymer having a particularly narrow molecular weight distribution.
In the report, it is described that there can be prepared a caprolactone polymer having a number average molecular weight ranging from 1,100 to 10,400 and a molecular weight distribution ranging from 1.10 to 1.16 which are measured with a GPC method in the presence of aluminum porphyrin complexes as a catalyst. It is to be noted that the terminology "immortal polymerization" is used in the report.
Furthermore, in Macromolecule Chemistry (Macromolecule Symposium) 42/43, 117-133 (1991), Okamoto has reported a process in which there can be prepared a polylactone diol polymer having a number average molecular weight of 3,000 or so and a molecular weight distribution ranging from 1.25 to 1.31 which are measured with a GPC method in the presence of ethylene glycol as an initiator and triethyloxonium hexafluorophosphonate as a catalyst.
Still further, Japanese Patent Examined publication (Kokoku) No. 56251/1991 discloses that polymers having a molecular weight distribution ranging from 1.54 to 1.76 which are measured with a GPC method in the presence of ethylene glycol as an initiator and halogenated stannous compounds in comparison with polymers prepared using conventional tetrabutyl titanate as a catalyst.
In addition, EP-A-0600417 discloses a process for the preparation of hydroxy-terminated linear carbonates having molecular weight distribution ranging from 1.7 to 2.1 by the reaction of polyvalent alcohols or hydroxy alkyl(meth)acrylates with cyclic carbonates in the presence of a catalyst selected from a Bronsted acid, an onium salt thereof, a strongly acidic ion exchange resin, an alkyl alkali metal, an alkali metal alkoxide, an amine, a tin compound, a tungsten compound, a titanium compound, and a zinc compound.
In the meantime, there have been desired a lactone polymer, carbonate polymer, and copolymer thereof having a narrow molecular weight distribution or a very high content of a (co)polymer component having a unitary structure in fields such as modifiers for resins, coatings, surface modifiers, adhesives, and pressure-sensitive adhesives, etc. In the fields, applications requiring a high added-value and an advanced performance in products have been recently increasing.
However, in an anionic polymerization process for the purpose of preparing a lactone polymer, carbonate polymer, and copolymer thereof having a specified structure, there must be employed a large amount of an organometallic compound as an initiator. As a result, there occur various problems that it is difficult to thermally control polymerization, and residual metallic components considerably deteriorate the thermal stability in the polymers, resulting in an adverse influence from the viewpoint of economy.
Specifically speaking, it is remarkably difficult to prepare a lactone polymer modified by a methacrylic group in which 2-hydroxyethylmethacrylate is allowed to react with from 1 to 5 mol of caprolactone according to single-stage anionic polymerization, resulting in an adverse influence from the viewpoint of economy.
Furthermore, in the above-described process in which aluminum porphyrin complexes are employed, it requires more than 10 days for preparation of the above-described caprolactone polymer and, further, the polymer obtained colors remarkably because the reaction rate is slow, resulting in it not being practical.
Still further, in the above-described process in which triethyloxonium hexafluorophosphonates are employed, it requires 24 hours at 30.degree. C. for preparing the above-described caprolactone diol polymer and, further, 5% or so of the lactone monomer remains. In the case when it is intended to raise the conversion of the lactone monomer to nearly 100%, it is a problem that the molecular weight distribution value may broaden.